Since a single Timer is used for several GenericObjectPool instances, this may create classloader issues and a memory leak of one classloader :
Let's imagine the following scenario :
- commons-pool.jar is in the classpath of a webapp container (e.g. tomcat).
- 2 webapps A and B are deployed, each creating an instance of GenericObjectPool for its own usage.
- each webapp makes use of the idle object evictor and sets a positive number for minIdle
- first, webapp A instantiates its GenericObjectPool. Since this is the first TimerTask to be created, the Timer instance is created, thus creating a Thread whose ContextClassLoader is the current one, that is webapp A's ContextClassLoader.
The TimerTask properly creates instances of idle objects in the pool, making use of the ObjectFactory provided by A.
- then B instantiates its GenericObjectPool. A new TimerTask is created, and it tries to invoke the ObjectFactory provided by B. But when it needs a class that only exists in B webapp, it cannot find it because the ContextClassLoader of the Timer Thread is A's classloader.
Other side effect : if webapp A is undeployed, but B is still running, then A's webappClassLoader cannot be GCed because the Timer Thread keeps a strong reference to A's classloader (as its context classloader).